The four surviving Russian astronauts of the first team to travel to space joined their current counterparts to celebrate the golden jubilee of the maiden flight.

The four surviving Russian astronauts of the first team to travel to space joined their current counterparts to celebrate the golden jubilee of the maiden flight.

Four of the twelve military pilots -- Valery Bykovsky, Boris Volynov, Viktor Gorbako and Alexei Leonov -- selected for Russia's first space mission in 1960s, recalled their experiences and difficulties during their training on Sunday.

"There were plenty of problems, from complex scientific and technical training to large physical strain," Gorbako told Itar-Tass.

In contrast to modern astronauts, the first batch were trained to withstand g-force of 12-point magnitude, the altitude of 14-15 kilometers with nothing but an oxygen mask and high temperatures.

"No one knew exactly what space flight conditions might be, so we were trained to face the worst," Gorbako said.

Initially, there were height and weight limitations on prospective astronauts -- their height has to be within 175 centimeters and weight not more than 70 kilograms. Now astronauts are 160-190 centimeters tall and of medium weight.

Earlier only military pilots can become astronauts whereas now the team has engineers and doctors as well.

Russia has two astronaut dynasties, the Volkovs and the Romanenkos. The appeal of being an astronaut professional has dipped much in the past 20 years, Cosmonaut Training Center head and holder of the world's record of space flight duration Sergei Krikalyov said.